Spin current magnetization rotational element, magnetoresistance effect element, and magnetic memory

ABSTRACT

A spin current magnetization rotational element including a first ferromagnetic metal layer in which a magnetization direction is variable, and a spin-orbit torque wiring that extends in a second direction intersecting a first direction that is a plane-orthogonal direction of the first ferromagnetic metal layer, and is joined to the first ferromagnetic metal layer. The first ferromagnetic metal layer has a lamination structure including a plurality of ferromagnetic constituent layers and a plurality of nonmagnetic constituent layers which are respectively interposed between the ferromagnetic constituent layers adjacent to each other. At least one ferromagnetic constituent layer among the plurality of ferromagnetic constituent layers has a film thickness different from a film thickness of the other ferromagnetic constituent layers, and/or at least one nonmagnetic constituent layer among the plurality of nonmagnetic constituent layers has a film thickness different from a film thickness of the other nonmagnetic constituent layers.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a spin current magnetizationrotational element, and more particularly, to a spin currentmagnetization reversal element. In addition, the disclosure also relatesto a magnetoresistance effect element and a magnetic memory.

Priority is claimed on Japanese Patent Application No. 2017-084537,filed Apr. 21, 2017, the content of which is incorporated herein byreference.

Description of Related Art

A giant magnetoresistive (GMR) element that is constituted by amulti-layer film of a ferromagnetic layer and a nonmagnetic layer, and atunnel magnetoresistive (TMR) element using an insulating layer (atunnel barrier layer, a barrier layer) as a nonmagnetic layer are known.Typically, the TMR element has higher element resistance in comparisonto the GMR element, but the magnetoresistance (MR) ratio of the TMRelement is greater than the MR ratio of the GMR element. According tothis, the TMR element has attracted attention as an element for amagnetic sensor, a high-frequency component, a magnetic head, and anonvolatile random access memory (MRAM).

The MRAM reads and writes data by using characteristics in which whenmagnetization directions of two ferromagnetic layers, between which aninsulating layer is provided, vary, element resistance of the TMRelement varies. As a recording type of the MRAM, a type in whichrecording (magnetization reversal) is performed by using a magneticfield formed by a current, and a type in which recording (magnetizationreversal) is performed by using spin transfer torque (STT) that occurswhen a current is allowed to flow in a lamination direction of amagnetoresistance effect element are known. The magnetization reversalof the TMR element which uses STT is efficient from the viewpoint ofenergy efficiency, but a reversal current density for magnetizationreversal is high. It is preferable that the reversal current density islow from the viewpoint of a long operational lifespan of the TMRelement. This preference is also true of the GMR element.

Accordingly, in recent years, as means for reducing a reversal currentwith a mechanism different from the STT, magnetization reversal using apure spin current generated by a spin hall effect has attractedattention (for example, refer to I. M. Miron, K. Garello, G. Gaudin, P.J. Zermatten, M. V. Costache, S. Auffret, S. Bandiera, B. Rodmacq, A.Schuhl, and P. Gambardella, Nature, 476, 189 (2011)). The pure spincurrent, which is generated by the spin hall effect, causes spin-orbittorque (SOT), and causes magnetization reversal by the SOT.Alternatively, in a pure spin current that is generated by an interfacerashba effect at an interface between different kinds of materials,magnetization reversal is caused by the same SOT. The pure spin currentis generated when the same numbers of upward spin electrons and downwardspin electrons flow in directions opposite to each other, and flows ofcharges are canceled. According to this, a current that flows to amagnetoresistance effect element is zero, and thus realization of amagnetoresistance effect element having a small reversal current densityis expected.

The spin hall effect depends on the magnitude of spin orbit interaction.In S. Fukami, T. Anekawa, C. Zhang, and H. Ohno, Nature Nanotechnology,DOI:10.1038/NNANO. 2016.29, Ta that is a heavy metal having a “d”electron that causes spin orbit interaction is used in a spin-orbittorque wiring. In addition, in GaAs that is a semiconductor, it is knownthat the spin orbit interaction occurs due to an electric field, whichis generated due to collapse of reversal symmetry, inside a crystal.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

According to S. Fukami, T. Anekawa, C. Zhang, and H. Ohno, NatureNanotechnology, DOI:10.1038/NNANO. 2016.29, it is reported that areversal current density by the SOT type is approximately the same as areversal current density by the STT type. However, the reversal currentdensity that is reported in the current SOT type is not sufficient torealize high integration and low energy consumption, and thus there isroom for improvement.

In addition, examples of a material that is used in the spin-orbittorque wiring (wiring that causes SOT and generates a pure spin current)of the magnetoresistance effect element of the SOT type include a heavymetal material including Ta similar to the material that is used in S.Fukami, T. Anekawa, C. Zhang, and H. Ohno, Nature Nanotechnology,DOI:10.1038/NNANO. 2016.29. The heavy metal material has high electricresistivity. Therefore, when the heavy material is used as a thin filmor a thin wire, there is a problem that power consumption is high.

The disclosure has been made in consideration of the above-describedproblem, and an object thereof is to provide a spin currentmagnetization rotational element, a magnetoresistance effect element,and a magnetic memory which are capable of reducing the current densityof magnetization rotation or magnetization reversal.

Means for Solving the Problems

In an SOT-type magnetoresistance effect element including a spin-orbittorque wiring, with respect to a current that intrudes into aferromagnetic metal layer that is a magnetization-free layer joined tothe spin-orbit torque wiring, the present inventors used a ferromagneticmetal layer having a lamination structure of [ferromagneticlayer/nonmagnetic layer]_(n) (n is the number of times of repetitivelamination) to make the lamination structure be an asymmetric structure,thereby avoiding or reducing cancellation of a pure spin current. As aresult, the prevent inventors have accomplished the disclosure in whichthe pure spin current that is generated is used for magnetizationrotation or magnetization reversal.

The disclosure provides the following means to accomplish the object.

(1) According to a first aspect of the disclosure, there is provided aspin current magnetization rotational element including: a firstferromagnetic metal layer in which a magnetization direction isvariable; and a spin-orbit torque wiring that extends in a seconddirection intersecting a first direction that is a plane-orthogonaldirection of the first ferromagnetic metal layer, and is joined to thefirst ferromagnetic metal layer. The first ferromagnetic metal layer hasa lamination structure including a plurality of ferromagneticconstituent layers and a plurality of nonmagnetic constituent layerswhich are respectively interposed between the ferromagnetic constituentlayers adjacent to each other. At least one ferromagnetic constituentlayer among the plurality of ferromagnetic constituent layers has a filmthickness different from the film thickness of the other ferromagneticconstituent layers, and/or at least one nonmagnetic constituent layeramong the plurality of nonmagnetic constituent layers has a filmthickness different from a film thickness of the other nonmagneticconstituent layers.

(2) In the spin current magnetization rotational element according tothe aspect, film thicknesses of two ferromagnetic constituent layers,between which one nonmagnetic constituent layer among the plurality ofnonmagnetic constituent layers is interposed, among the plurality offerromagnetic constituent layers may be different from each other, orfilm thicknesses of two nonmagnetic constituent layers, between whichone ferromagnetic constituent layer among the plurality of ferromagneticconstituent layers is interposed, among the plurality of nonmagneticconstituent layers may be different from each other.

(3) In the spin current magnetization rotational element according tothe aspect, among the plurality of nonmagnetic constituent layers, anonmagnetic laminated layer that is the closest to the spin-orbit torquewiring may be thinner than the other nonmagnetic laminated layers.

(4) In the spin current magnetization rotational element according tothe aspect, among the plurality of nonmagnetic constituent layers, amaterial of at least one nonmagnetic constituent layer may be differentfrom a material of the other nonmagnetic constituent layers.

(5) In the spin current magnetization rotational element according tothe aspect, the nonmagnetic constituent layers may be formed from amaterial that applies interface-orthogonal magnetic anisotropy to theferromagnetic constituent layers.

(6) In the spin current magnetization rotational element according tothe aspect, among the plurality of ferromagnetic constituent layers, aferromagnetic constituent layer that is closest to the spin-orbit torquewiring may be thinner than the other ferromagnetic constituent layers.

(7) In the spin current magnetization rotational element according tothe aspect, any one ferromagnetic constituent layer among the pluralityof ferromagnetic constituent layers may include a dead layer.

(8) In the spin current magnetization rotational element according tothe aspect, with respect to an average film thickness of the pluralityof ferromagnetic constituent layers, a film thickness of each of theferromagnetic constituent layers may be different from the average filmthickness by ±10% or more, or with respect to an average film thicknessof the plurality of nonmagnetic constituent layers, the film thicknessof each of nonmagnetic laminated layers may be different from theaverage film thickness of the nonmagnetic laminated layers by ±10% ormore.

(9) In the spin current magnetization rotational element according tothe aspect, as the first ferromagnetic metal layer is closer to thespin-orbit torque wiring, a cross-sectional area of a cross-section thatis orthogonal to the first direction may be enlarged.

(10) In the spin current magnetization rotational element according tothe aspect, the sheet resistance of the first ferromagnetic metal layermay be smaller than the sheet resistance of the spin-orbit torquewiring.

(11) In the spin current magnetization rotational element according tothe aspect, a material of the ferromagnetic constituent layers may beselected from ferromagnetic metals including any one of Fe, Co, and Ni,and a material of the nonmagnetic constituent layers may be selectedfrom nonmagnetic metals including any one of Ti, Cr, Cu, Mo, Ru, Rh, Pd,Ag, Hf, Ta, W, Ir, Pt, Au, and Bi.

(12) In the spin current magnetization rotational element according tothe aspect, the ratio of the length of the first ferromagnetic metallayer along the second direction to the thickness of the firstferromagnetic metal layer may be 1 or greater.

(13) According to a second aspect of the disclosure, there is provided amagnetoresistance effect element including: the spin currentmagnetization rotational element according to the aspect; a secondferromagnetic metal layer in which a magnetization direction is fixed;and a nonmagnetic layer that is interposed between the firstferromagnetic metal layer and the second ferromagnetic metal layer.

(14) In the magnetoresistance effect element according to the aspect,among the plurality of ferromagnetic constituent layers, the filmthickness of a ferromagnetic constituent layer that is in contact withthe nonmagnetic layer may be the smallest.

(15) According to a third aspect of the disclosure, there is provided amagnetic memory including a plurality of the magnetoresistance effectelements according to the aspect.

Effects of the Invention

According to the spin current magnetization rotational element of thedisclosure, it is possible to provide a spin current magnetizationrotational element capable of reducing the current density ofmagnetization rotation or magnetization reversal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views of an example of a spin currentmagnetization rotational element according to an embodiment of thedisclosure, and in the drawings, FIG. 1A is a plan view, and FIG. 1B isa cross-sectional view taken along line X-X that is a central line of aspin-orbit torque wiring shown in FIG. 1A in a width direction;

FIG. 2 is a schematic view showing a spin hall effect;

FIG. 3 is a schematic view showing an operation principle of thedisclosure;

FIGS. 4A to 4D are schematic cross-sectional views of a firstferromagnetic metal layer in another example of the spin currentmagnetization rotational element of the disclosure;

FIGS. 5A to 5F are schematic cross-sectional views of a firstferromagnetic metal layer in still another example of the spin currentmagnetization rotational element of the disclosure; and

FIG. 6 is a perspective view schematically showing a magnetoresistanceeffect element that is an application example of the spin currentmagnetization rotational element of the disclosure and is also amagnetoresistance effect element according to an embodiment of thedisclosure.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the disclosure will be described in detail with referenceto the accompanying drawings in an appropriate manner. Drawings used inthe following description may show a characteristic portion in anenlarged manner for easy understanding of characteristics of thedisclosure for convenience, and dimensional ratios and the like ofrespective constituent elements may be different from actual dimensionalratios and the like. Materials, dimensions, and the like which areexemplary examples in the following description are illustrative only,and the disclosure is not limited thereto. The disclosure can be carriedout by appropriately making modifications in a range that exhibits aneffect of the disclosure. In elements of the disclosure, another layermay be provided in a range that exhibits the effect of the disclosure.

Spin Current Magnetization Rotational Element

FIGS. 1A and 1B are schematic views showing an example of a spin currentmagnetization rotational element according to an embodiment of thedisclosure. FIG. 1A is a plan view, and FIG. 1B is a cross-sectionalview taken along line X-X that is a central line of a spin-orbit torquewiring 2 in FIG. 1A in a width direction.

A spin current magnetization rotational element 10 shown in FIGS. 1A and1B includes a first ferromagnetic metal layer 1 in which a magnetizationdirection is variable, and a spin-orbit torque wiring 2 that extends ina second direction intersecting a first direction that is aplane-orthogonal direction of the first ferromagnetic metal layer 1 andis joined to the first ferromagnetic metal layer 1. The firstferromagnetic metal layer 1 has a lamination structure including aplurality of ferromagnetic constituent layers 1Aa, 1Ab, and 1Ac, and aplurality of nonmagnetic constituent layers 1Ba and 1Bb which arerespectively interposed between the ferromagnetic constituent layersadjacent to each other. That is, first ferromagnetic metal layer 1 has alamination structure including a plurality of ferromagnetic constituentlayers 1Aa, 1Ab, and 1Ac, and a plurality of nonmagnetic constituentlayers 1Ba and 1Bb, each of the plurality of nonmagnetic constituentlayers 1Ba and 1Bb being sandwiched between two of the plurality offerromagnetic constituent layers 1Aa, 1Ab, and 1Ac adjacent each other.the At least one ferromagnetic constituent layer among the plurality offerromagnetic constituent layers has a film thickness different fromthat of the other ferromagnetic constituent layers, and/or at least onenonmagnetic constituent layer 1Ba between the plurality of nonmagneticconstituent layers 1Ba and 1Bb has a film thickness different from thatof the other nonmagnetic constituent layer 1Bb.

Hereinafter, the plane-orthogonal direction of the first ferromagneticmetal layer 1 or a direction (first direction) in which the firstferromagnetic metal layer 1 and the spin-orbit torque wiring 2 arelaminated is set as a z-direction, a direction (second direction) thatis orthogonal to the z-direction and is parallel to the spin-orbittorque wiring 2 is set as an x-direction, and a direction (thirddirection) orthogonal to the x-direction and the z-direction is set as ay-direction.

In the following description including FIGS. 1A and 1B, as an example ofa configuration in which the spin-orbit torque wiring 2 extends in adirection intersecting the first direction that is a plane-orthogonaldirection of the first ferromagnetic metal layer 1, a description willbe given of a case of a configuration extending in a direction that isorthogonal to the first direction.

In the spin current magnetization rotational element of the embodiment,a current is allowed to flow to a spin-orbit torque wiring to generate apure spin current, and the pure spin current is diffused to a firstferromagnetic metal layer that is in contact with the spin-orbit torquewiring. According to this, magnetization rotation of the firstferromagnetic metal layer is caused to occur by a spin-orbit torque(SOT) effect due to the pure spin current. In addition, the firstferromagnetic metal layer is formed in a predetermined laminationstructure. According to this, a pure spin current is generated by acurrent that invades into the first ferromagnetic metal layer amongcurrents which are allowed to flow to the spin-orbit torque wiring, andthe pure spin current is also used in magnetization rotation, therebyreducing a reversal current density. When the SOT effect is sufficientlylarge, magnetization of the first ferromagnetic metal layer 1 isreversed. In this case, the spin current magnetization rotationalelement of the embodiment can be particularly referred to as “spincurrent magnetization reversal element” as described above.

In the spin current magnetization rotational element of the embodiment,a pure spin current due to an interface rashba effect is also used.Although a detailed mechanism of the interface rashba effect is notclear, the mechanism is considered as follows. At an interface betweendifferent kinds of materials, it is considered that space reversalsymmetry collapses and thus a potential gradient exists in aplane-orthogonal direction. In a case where a current flows along aninterface in which a potential gradient exists in a plane-orthogonaldirection, that is, in a case where electrons move in a two-dimensionalplane, an effective magnetic field acts on a spin in an in-planedirection orthogonal to a movement direction of electrons, and thusdirections of the spin are arranged in the effective magnetic field.According to this, spin accumulation occurs in the interface. Inaddition, the spin accumulation causes a pure spin current, which isdiffused to the outside of a plane, to occur.

At an interface between a ferromagnetic constituent layer and anonmagnetic constituent layer which constitute the first ferromagneticmetal layer, spin accumulation (a state in which either an upward spinor a downward spin is rich) occurs due to the interface rashba effect,and the spin accumulation causes a pure spin current to occur. The purespin current also contributes to magnetization rotation.

The spin current magnetization rotational element of the embodiment,that is, an element that performs magnetization rotation of aferromagnetic metal layer by the SOT effect by the pure spin current canbe used in a magnetoresistance effect element that performsmagnetization reversal of the ferromagnetic metal layer by only SOT dueto the pure spin current, and in this case, the spin currentmagnetization rotational element can be particularly referred to as“spin current magnetization reversal element”. In addition, the spincurrent magnetization rotational element of the embodiment can be usedin a magnetoresistance effect element that uses STT in the related artas assist means or main means of magnetization reversal of theferromagnetic metal layer.

Spin-Orbit Torque Wiring

The spin-orbit torque wiring 2 is formed from a material in which, whena current flows, a pure spin current is generated due to a spin halleffect. It is sufficient for the material to have a configuration inwhich a pure spin current is generated in the spin-orbit torque wiring2.

The spin hall effect is a phenomenon in which, when a current flows to amaterial, a pure spin current is caused in a direction orthogonal to adirection of the current on the basis of spin orbit interaction.

FIG. 2 is a schematic view showing the spin hall effect. FIG. 2 is across-sectional view obtained by cutting the spin-orbit torque wiring 2shown in FIGS. 1A and 1B along the x-direction. A description will begiven of a mechanism in which the pure spin current is generated due tothe spin hall effect with reference to FIG. 2.

As shown in FIG. 2, when a current I is allowed to flow in an extensiondirection of the spin-orbit torque wiring 2, a first spin S1 that isoriented to a front side on a paper surface and a second spin S2 that isoriented to a back side on the paper surface are curved in a directionorthogonal to the current. A typical hall effect and the spin halleffect are common in that a movement (migration) direction of moving(migrating) charges (electrons) can be curved. However, in the typicalhall effect, when receiving a Lorentz force, the movement direction ofcharged particles, which move in a magnetic field, can be curved. Incontrast, in the spin hall effect, although the magnetic field does notexist, only when an electron migrates (only when a current flows), themigration direction of the electron can be curved. In this regard, thetypical hall effect and the spin hall effect are greatly different fromeach other.

In a nonmagnetic substance (a material that is not a ferromagneticsubstance), the number of electrons of the first spin S1, and the numberof electrons of the second spin S2 are the same as each other.Accordingly, the number of electrons of the first spin S1 that faces anupward direction in the drawing, and the number of electrons of thesecond spin S2 that faces a downward direction are the same as eachother. According to this, a current as a net flux of charges is zero. Aspin current that is not accompanied with the current is particularlyreferred to as “pure spin current”.

In a case where a current is allowed to flow through a ferromagneticsubstance, the first spin S1 and the second spin S2 are curved indirections opposite to each other. In this regard, nonmagnetic substanceand the ferromagnetic substance are the same as each other. On the otherhand, in the ferromagnetic substance, either the first spin S1 or thesecond spin S2 is rich, and as a result, a net flux of charges occurs (avoltage occurs). In this regard, the nonmagnetic substance and theferromagnetic substance are different from each other. Accordingly, as amaterial of the spin-orbit torque wiring 2, a material composed of aferromagnetic substance alone is not included.

Here, when a flow of electrons of the first spin S1 is set as J_(↑), aflow of electrons of the second spin S2 is set as J_(↓), and a spincurrent is set as J_(S), J_(S) is defined as J_(↑)-J_(↓). In FIG. 2,J_(S) as the pure spin current flows in an upward direction in thedrawing. Here, J_(S) represents a flow of electrons in whichpolarizability is 100%.

In FIGS. 1A and 1B, when a ferromagnetic substance is brought intocontact with a top surface of the spin-orbit torque wiring 2, the purespin current is diffused and flows into the ferromagnetic substance.That is, a spin is injected into the first ferromagnetic metal layer 1.

A material of the spin-orbit torque wiring may be a material capable ofgenerating the pure spin current, and examples thereof include aconfiguration including a plurality of kinds of material portions.

The material of the spin-orbit torque wiring can be a material that isselected from the group consisting of tungsten, rhenium, osmium,iridium, and alloys including at least one or more of the metals. Inaddition, tungsten, rhenium, osmium, and iridium have a 5d electron inthe outermost shell, and have a large orbital angular momentum in a casewhere five orbits of a “d” orbit are in degeneracy. According to this,the spin orbit interaction that causes the spin hall effect to occurincreases, and thus it is possible to efficiently generate a spincurrent.

The material of the spin-orbit torque wiring may include a nonmagneticheavy metal.

Here, the heavy metal represents a metal having a specific gravity equalto or greater than the specific gravity of yttrium.

In this case, it is preferable that the nonmagnetic heavy metal is anonmagnetic metal that has an atomic number higher than 39 and has a “d”electron or an “f′ electron in the outermost shell. The reason of thepreference is because in the nonmagnetic metal, the spin orbitinteraction that causes the spin hall effect to occur is great. Thespin-orbit torque wiring may be formed from only a nonmagnetic metalthat has an atomic number of 39 or higher and has a “d” electron” or an“f” electron in the outermost shell.

Typically, when a current is allowed to flow through a metal, theentirety of electrons move in a direction opposite to a direction of thecurrent regardless of a direction of a spin. In contrast, in thenonmagnetic metal that has a “d” electron or an “f” electron in theoutermost shell and has a high atomic number, the spin orbit interactionis great, and thus a direction in which electrons move due to the spinhall effect depends on a direction of the spin of the electrons. As aresult, the pure spin current is likely to occur.

When it is assumed that a low resistance portion is formed from Cu (1.7μΩcm), examples of a material, which has an atomic number of 39 orhigher and in which electrical resistivity is two or more timeselectrical resistivity of Cu, include Y, Zr, Nb, Mo, Ru, Pd, Cd, La, Hf,Ta, W, Re, Os, Ir, Pt, Hg, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, and Lu.

In a case where the material of the spin-orbit torque wiring includes anonmagnetic heavy metal, the material may include the heavy metalcapable of generating the pure spin current in a limited amount. Inaddition, in this case, in the spin-orbit torque wiring, it ispreferable that the heavy metal capable of generating the pure spincurrent is in a sufficiently small concentration region in comparison toa main component, or the heavy metal capable of generating the pure spincurrent is a main component, for example, 90% or greater. In this caseof a heavy metal, it is preferable that the heavy metal capable ofgenerating the pure spin current is composed of 100% of a nonmagneticmetal that has a “d” electron or an “f” electron in the outermost shelland an atomic number of 39 or higher.

Here, description of “the heavy metal capable of generating the purespin current is in a sufficiently small concentration region incomparison to a main component of the spin-orbit torque wiring”represents that for example, in a spin-orbit torque wiring includingcopper as a main component, a concentration of the heavy metal is 10% orless in terms of a molar ratio. In a case where the main component thatconstitutes the spin-orbit torque wiring is composed of a material otherthan the above-described heavy metal, a concentration of a heavy metalthat is included in the spin-orbit torque wiring is preferably 50% orless in terms of a molar ratio, and more preferably 10% or less. Thisconcentration region is a region capable of effectively obtaining a spinscattering effect of electrons. In a case where the concentration of theheavy metal is low, a light metal having an atomic number lower thanthat of the heavy metal becomes a main component. Furthermore, in thiscase, it is assumed that the heavy metal does not form an alloy with thelight metal, and atoms of the heavy metal are dispersed in the lightmetal in disorder. In the light metal, the spin orbit interaction isweak, and thus generation of the pure spin current due to the spin halleffect is less likely to occur. However, when electrons pass through theheavy metal in the light metal, a spin scattering effect also exists atan interface between the light metal and the heavy metal, and thus it ispossible to efficiently generate the pure spin current even in a regionin which the concentration of the heavy metal is low. When theconcentration of the heavy metal is greater than 50%, a ratio of thespin hall effect in the heavy metal increases, but the effect of theinterface between the light metal and the heavy metal decreases, andthus a total effect decreases. Accordingly, it is preferable that theheavy metal has a concentration to a certain extent capable of expectinga sufficient interface effect.

In addition, as the material of the spin-orbit torque wiring, a magneticmetal may also be included. The magnetic metal represents aferromagnetic metal or an antiferromagnetic metal. The reason for thisis because when a slight amount of magnetic metal is included in thenonmagnetic metal, the spin orbit interaction is enhanced, and thus itis possible to raise spin current generation efficiency with respect toa current that is allowed to flow to the spin-orbit torque wiring. Thespin-orbit torque wiring may be formed from only the antiferromagneticmetal. The antiferromagnetic metal can obtain approximately the sameeffect as in a case where the heavy metal is composed of 100% of anonmagnetic metal that has a “d” electron or an “f” electron in theoutermost shell and has an atomic number of 39 or higher. As theantiferromagnetic metal, for example, IrMn and PtMn are preferable, andIrMn that is stable against heat is more preferable.

The spin orbit interaction occurs due to a substance specific to aninternal field of a spin-orbit torque wiring material, and thus the purespin current also occurs in a nonmagnetic material. When a slight amountof a magnetic metal is added to the spin-orbit torque wiring material,the magnetic metal scatters an electron spin that flows, and thus spincurrent generation efficiency is improved. However, the amount of themagnetic metal added too increases, the pure spin current that isgenerated is scattered by the magnetic metal that is added, and as aresult, an operation of reducing the spin current becomes strong.Accordingly, it is preferable that a molar ratio of the magnetic metalthat is added is sufficiently smaller than a molar ratio of a maincomponent of the spin-orbit torque wiring. That is, it is preferablethat the molar ratio of the magnetic metal that is added is 3% or less.

In addition, the spin-orbit torque wiring may include a topologicalinsulator. The spin-orbit torque wiring may be composed of only thetopological insulator. The topological insulator is a substance of whichthe inside is an insulator or a high-resistance substance, but aspin-polarized metal state occurs on a surface thereof. In thesubstance, spin orbit interaction similar to an internal magnetic fieldexists. Accordingly, even though an external magnetic field does notexist, a new topological phase is exhibited due to an effect of the spinorbit interaction. This phase is the topological insulator, and it ispossible to generate the pure spin current with high efficiency due tostrong spin orbit interaction and collapse of reversal symmetry at anedge.

As the topological insulator, for example, SnTe,Bi_(1.5)Sb_(0.5)Te_(1.7)Se_(1.3), TlBiSe₂, Bi₂Te₃, (Bi_(1-x)Sb_(x))₂Te₃,and the like are preferable. The topological insulators can generate aspin current with high efficiency.

In the spin current magnetization rotational element of the embodiment,a current (SOT reversal current) that is allowed to flow to thespin-orbit torque wiring so as to use the SOT effect is a typicalcurrent that is accompanied with a flow of charges, and thus when thecurrent is allowed to flow, Joule's heat is generated.

Here, a heavy metal that is a material that is likely to generate thepure spin current has electrical resistivity higher than that of a metalthat is used as a typical wiring.

According to this, it is preferable that the spin-orbit torque wiringincludes a portion having low electrical resistivity in comparison to acase where the entirety of the spin-orbit torque wiring is formed from amaterial capable of generating the pure spin current from the viewpointof reducing the Joule's heat due to the SOT reversal current. In thisregard, the spin-orbit torque wiring that is provided in the spincurrent magnetization rotational element of the embodiment may include aportion (pure spin current generating portion) that is formed from amaterial that generate the pure spin current, and a portion(low-resistance portion) that is formed from a material havingelectrical resistivity lower than that of the pure spin currentgenerating portion.

In this case, as a material of the pure spin current generating portion,materials which are described above as the material of the spin-orbittorque wiring can be used, and as a material of the low-resistanceportion, a material that is used as a typical wiring can be used. Forexample, aluminum, silver, copper, gold, and the like can be used. Thelow-resistance portion may be composed of a material having electricalresistivity lower than that of the pure spin current generating portion,and for example, a configuration composed of a plurality of kinds ofmaterial portions and the like are possible.

Furthermore, the pure spin current may be generated at thelow-resistance portion. In this case, with regard to discriminationbetween the pure spin current generating portion and the low-resistanceportion, portions composed of materials, which are described asmaterials of the pure spin current generating portion and thelow-resistance portion in this specification, may be noted as the purespin current generating portion or the low-resistance portion fordiscrimination. In addition, as a portion other than a main portion thatgenerates the pure spin current, a portion having electrical resistivitylower than that of the main portion may be noted as the low-resistanceportion for discrimination from the pure spin current generatingportion.

In the embodiment, description has been given of a case where thespin-orbit torque wiring is directly connected to the firstferromagnetic metal layer. However, as to be described later, anotherlayer such as a cap layer may be interposed between the firstferromagnetic metal layer and the spin-orbit torque wiring. Details ofthe cap layer will be described in relation to a cap layer 104 in anapplication of the magnetoresistance effect element.

First Ferromagnetic Metal Layer

The first ferromagnetic metal layer 1 shown in FIGS. 1A and 1B has alamination structure including three ferromagnetic constituent layers1Aa, 1Ab, and 1Ac, the nonmagnetic constituent layer 1Ba that isinterposed between the ferromagnetic constituent layers 1Aa and 1Abadjacent to each other, and the nonmagnetic constituent layer 1Bb thatis interposed between the ferromagnetic constituent layers 1Ab and 1Acadjacent to each other. However, the first ferromagnetic metal layer mayhave a configuration, in which among the plurality of ferromagneticconstituent layers, at least one ferromagnetic constituent layer has afilm thickness different from that of the other ferromagneticconstituent layers, a configuration in which among the plurality ofnonmagnetic constituent layers, at least one nonmagnetic constituentlayer has a film thickness different from that of the other nonmagneticconstituent layers, or a configuration in which at least oneferromagnetic constituent layer has a film thickness different from thatof the other ferromagnetic constituent layers, and at least onenonmagnetic constituent layer has a film thickness different from thatof the other nonmagnetic constituent layers.

In the spin current magnetization rotational element of the embodiment,it is preferable that film thicknesses of two ferromagnetic constituentlayers between which one nonmagnetic constituent layer among theplurality of nonmagnetic constituent layers constituting the firstferromagnetic metal layer is interposed, is different from each other,or film thicknesses of two nonmagnetic constituent layers, between whichone ferromagnetic constituent layer among the plurality of ferromagneticconstituent layers constituting the first ferromagnetic metal layer isinterposed, is different from each other.

Furthermore, in a case where consideration is made only to the pure spincurrent due to the spin hall effect, the film thicknesses of thenonmagnetic constituent layers may be made to be different from eachother, but the magnitude of the interface rashba effect depends on thefilm thickness of the ferromagnetic constituent layers. Accordingly, ina configuration in which the film thicknesses of the ferromagneticconstituent layers are made to be different from each other, it is alsopossible to increase the pure spin current.

Ferromagnetic Constituent Layer

As a material of the ferromagnetic constituent layers 1Aa, 1Ab, and 1Acwhich constitute the first ferromagnetic metal layer 1, a ferromagneticmaterial, particularly, a soft-magnetic material, can be used. Forexample, a metal selected from the group consisting of Cr, Mn, Co, Fe,and Ni, an alloy that includes one or more kinds of the metals, an alloythat includes the metals and at least one or more elements among B, C,and N, and the like can be used. Specific examples thereof includeCo—Fe, Co—Fe—B, and Ni—Fe.

In a case where a magnetization direction of the ferromagneticconstituent layers 1Aa, 1Ab, and 1Ac is set to be orthogonal to alamination surface, it is preferable that the film thickness of each ofthe ferromagnetic constituent layers is set to be 1.5 nm or less. At aninterface between the ferromagnetic constituent layers and thenonmagnetic constituent layers, it is possible to apply orthogonalmagnetic anisotropy (interface-orthogonal magnetic anisotropy) to theferromagnetic constituent layers. In addition, when the film thicknessof the ferromagnetic constituent layers is set to be large, an effect ofthe interface orthogonal magnetic anisotropy is attenuated, and thus itis preferable that the film thickness of the ferromagnetic constituentlayer is set to be small.

It is preferable that the film thickness of each of the ferromagneticconstituent layer is set to be 1.0 nm or less. The reversal currentdensity due to SOT is proportional to the film thickness of theferromagnetic metal layer, and thus it is possible to reduce thereversal current density while maintaining relatively stronginterface-orthogonal magnetic anisotropy.

In the spin current magnetization rotational element of the disclosure,it is preferable that among the plurality of ferromagnetic constituentlayers, a ferromagnetic constituent layer that is closest to thespin-orbit torque wiring is thinner than the other ferromagneticconstituent layers.

When the ferromagnetic constituent layer that is closest to thespin-orbit torque wiring is made to be thin, it is possible to increasethe interface-orthogonal magnetic anisotropy that acts between thespin-orbit torque wiring and the ferromagnetic constituent layer, andthus it is possible to realize a relatively strong orthogonalmagnetization film.

In the spin current magnetization rotational element of the disclosure,any one ferromagnetic constituent layer among the plurality offerromagnetic constituent layers may include a dead layer.

Here, the dead layer represents a region in a state in which elementsare mixed at the interface between the nonmagnetic constituent layer andthe spin-orbit torque wiring, and thus magnetization is not present.

When the ferromagnetic constituent layer includes the dead layer, aneffective film thickness of the ferromagnetic constituent layer ischanged from a design value, and as a result, it is possible to changethe degree of asymmetry of the lamination structure.

Furthermore, presence of the dead layer can be confirmed as follows.That is, when reducing the film thickness of the ferromagneticconstituent layer with respect to magnetization, a portion correspondingto a film thickness that remains when the magnetization becomes zero isconfirmed as the dead layer.

In the spin current magnetization rotational element of the embodiment,it is preferable that as the first ferromagnetic metal layer is closerto the spin-orbit torque wiring, a cross-sectional area of across-section orthogonal to the first direction (plane-orthogonaldirection) is enlarged.

When the first ferromagnetic metal layer is cut along a plane orthogonalto the plane-orthogonal direction, if a cross-sectional area is largerat a portion that is close to the spin-orbit torque wiring, resistancebecomes lower in comparison to an element having a configuration inwhich the cross-sectional area is the same in the plane-orthogonaldirection, and thus a current is likely to invade into the firstferromagnetic metal layer.

Nonmagnetic Constituent Layer

The nonmagnetic constituent layers 1Ba and 1Bb are layers (spin currentgenerating layers) which generate a spin current.

Accordingly, as a material of the nonmagnetic constituent layers 1Ba and1Bb, materials which are described above as the material of thespin-orbit torque wiring can be used.

It is preferable that the film thickness of each of the nonmagneticconstituent layers is set to 0.3 to 2.0 nm. When the film thickness issmaller than 0.3 nm, the film thickness becomes a film thickness whencutting one atomic layer, and thus there is a concern thatinterface-orthogonal magnetic anisotropy may not be caused. When thefilm thickness is larger than 2.0 nm, there is a concern that magneticbonding between the ferromagnetic constituent layers is broken, and thusthe first ferromagnetic metal layer may not function as oneferromagnetic metal layer.

In the spin current magnetization rotational element of the embodiment,among the plurality of nonmagnetic constituent layers, a nonmagneticconstituent layer that is closest to the spin-orbit torque wiring may bethinner than the other nonmagnetic constituent layers.

A current flows most strongly in the nonmagnetic constituent layerclosest to the spin-orbit torque wiring. Accordingly, when thenonmagnetic constituent layer is the thinnest, an effect of generatingthe pure spin current due to the spin hall effect can be exhibited themost.

Furthermore, the effect depends on resistivity of the nonmagneticconstituent layers. It is preferable that a material of the nonmagneticconstituent layer have a resistivity lower than the resistivity of amaterial of the ferromagnetic constituent layers. For example, in a casewhere the material of the ferromagnetic constituent layers is Fe,resistivity is 8.9 μΩ·cm. Accordingly, examples of a preferred materialof the nonmagnetic constituent layers include W (4.9 μΩ·cm), Ag (1.47μΩ·cm), Au (2.05 μΩ·cm), Ir (4.7 μΩ·cm), Os (8.1 μΩ·cm), Mo (5 μΩ·cm),Rh (4.3 μΩ·cm), and the like.

With regard to the plurality of nonmagnetic constituent layers, it isconsidered that the magnitude of a current that flows to the nonmagneticconstituent layers is different in accordance with a distance from thespin-orbit torque wiring, but it is difficult to estimate the dependencyat this point of time. Accordingly, it is preferable to optimize acombination of the film thicknesses of the nonmagnetic constituentlayers by measuring the magnitude of magnetization rotation. This isalso true of the plurality of ferromagnetic constituent layers.

In the spin current magnetization rotational element of the embodiment,among the plurality of nonmagnetic constituent layers, a material of atleast one nonmagnetic constituent layer may be different from a materialof the other nonmagnetic constituent layers.

In a configuration of different kinds of materials, it is possible toobtain an asymmetric lamination structure, and thus it is possible tomaximize the SOT effect.

In the spin current magnetization rotational element of the embodiment,it is preferable that the nonmagnetic constituent layers are formed froma material that applies interface-orthogonal magnetic anisotropy to theferromagnetic constituent layers.

When using the material having the interface-orthogonal magneticanisotropy, it is possible to improve the orthogonal magnetic anisotropyof the first ferromagnetic metal layer. In the lamination structure, anorthogonal magnetization film is obtained, and thus it is possible toapply the degree of integration in a case of MRAM.

Operation Principle

The operation principle of the spin current magnetization rotationalelement of the embodiment will be described with reference to FIGS. 1Aand 1B.

The first ferromagnetic metal layer is formed from a metal, and thuswhen currents flow to the spin-orbit torque wiring, the current alsoinvades into the first ferromagnetic metal layer. Parts of the currentswhich invade into the first ferromagnetic metal layer also flow to thenonmagnetic constituent layers 1Ba and 1Bb (Ia and Ib). When thecurrents flow to the nonmagnetic constituent layers 1Ba and 1Bb, anelectron of upward spin and an electron of downward spin are curved indirections opposite to each other due to the spin hall effect, and thusthe pure spin current can be generated.

FIG. 3 is a view schematically showing movement of a spin due to thespin hall effect in a case where the same current flows to twononmagnetic constituent layers 11Ba and 11Bb in a lamination structureincluding three ferromagnetic constituent layers 11Aa, 11Ab, and 11Acwhich are formed from the same material and have the same filmthickness, and the two nonmagnetic constituent layers 11Ba and 11Bbwhich are formed from the same material and have the same filmthickness.

In the lamination structure including a plurality of ferromagneticconstituent layers which are formed from the same material and have thesame film thickness, and a plurality of nonmagnetic constituent layerswhich are formed from the same material and have the same film thickness(hereinafter, the lamination structure may be referred to as “symmetriclamination structure”), spin currents in directions opposite to eachother meet in the vicinity of a portion indicated by a dotted-linecircle, and spin currents are canceled. As a result, the pure spincurrent is not generated, or the pure spin current becomes weak.

A lamination structure of [ferromagnetic layer/nonmagnetic layer]_(n) isa configuration that is used as a method of generating orthogonalmagnetic anisotropy in the related art, but a symmetric laminationstructure is assumed. Accordingly, it is recognized that the pure spincurrent is not generated as a result of cancelation.

The present inventors collapses “symmetric lamination structure” (thatis, employs “asymmetric lamination structure”) so that spin currents indirections opposite to other are not canceled so as to generate the purespin current, and uses the pure spin current in magnetization rotation.The “asymmetric lamination structure” represents a configuration inwhich film thicknesses are set to be different from each other in orderfor the spin currents in directions opposite to each other not to becanceled. The “asymmetric lamination structure” may be realized byemploying materials different from each other, or may be realized by acombination of materials different from each other and film thicknessesdifferent from each other.

The spin current magnetization rotational element 10 shown in FIGS. 1Aand 1B employs a configuration in which the nonmagnetic constituentlayer 1Ba has a film thickness larger than that of the nonmagneticconstituent layer 1Bb, and thus spin currents in directions opposite toeach other are not canceled, and thus a pure spin current Js₂ isgenerated. In addition, the three ferromagnetic constituent layers havethe same film thickness.

In the spin current magnetization rotational element 10, magnetizationrotation of the ferromagnetic constituent layers is performed by a purespin current Js₁ that is generated in the spin-orbit torque wiring andthe pure spin current Js₂ that is generated in the first ferromagneticmetal layer. The pure spin current Js₁ and the pure spin current Js₂also include a pure spin current based on the interface rashba effect.

FIGS. 4A to 4D are schematic cross-sectional views of a firstferromagnetic metal layer in another example of the spin currentmagnetization rotational element of the embodiment. It is assumed thatthe spin-orbit torque wiring is disposed on a lower side of thedrawings.

The first ferromagnetic metal layer shown in FIGS. 4A to 4D correspondsto a case of a lamination structure including three ferromagneticconstituent layers and two nonmagnetic constituent layers. For example,in a case where the ferromagnetic constituent layers are formed from Co,and the nonmagnetic constituent layers are formed from Pt, thelamination structure corresponds to a case of [Co/Pt]₂/Co.

FIG. 4A shows an example of a case where the three ferromagneticconstituent layers have the same film thickness, and the two nonmagneticconstituent layers have film thicknesses different from each other.Differently from the example in FIGS. 1A to 1B, FIG. 4A corresponds to acase where between the nonmagnetic constituent layers, the filmthickness of a nonmagnetic constituent layer that is far away from thespin-orbit torque wiring is larger than the film thickness of anonmagnetic constituent layer that is closer to the spin-orbit torquewiring. In FIGS. 4A to 4D, t1, t2, and t3 represent thicknesses of therespective layers.

FIGS. 4B to 4D are examples of a case where the two nonmagneticconstituent layers have the same film thickness, and the threeferromagnetic constituent layers have film thicknesses different fromeach other.

A configuration of FIG. 4B is an example in which the film thicknessgradually becomes smaller as it goes from the uppermost layer to thelowest layer. In film-thickness magnitude relationship described on aright side in FIG. 4B, the uppermost magnitude relationship correspondsto FIG. 4B, and the other three magnitude relationships correspond tomodification examples of FIG. 4B.

A configuration of FIG. 4C is an example in which the film thicknessgradually becomes larger as it goes from the uppermost layer to thelowest layer. Among film-thickness magnitude relationships described ona right side in FIG. 4C, the uppermost magnitude relationshipcorresponds to FIG. 4C, and the other three magnitude relationshipscorrespond to modification examples of FIG. 4C.

A configuration of FIG. 4D is an example in which arrangement of thefilm thickness does not follow a large film thickness order or a smallfilm thickness order. Among film-thickness relationships described on aright side in FIG. 4D, the uppermost relationship corresponds to FIG.4D, and the other two relationships correspond to modification examplesof FIG. 4D.

FIGS. 5A to 5F are schematic cross-sectionals views of a firstferromagnetic metal layer in still another example of the spin currentmagnetization rotational element of the embodiment. It is assumed thatthe spin-orbit torque wiring is disposed on a lower side in thedrawings.

The first ferromagnetic metal layer shown in FIGS. 5A to 5F correspondsto a case of a lamination structure including four ferromagneticconstituent layers and three nonmagnetic constituent layers. Forexample, in a case where the ferromagnetic constituent layers are formedfrom Co, and the nonmagnetic constituent layers are formed from Pt, thelamination structure corresponds to a case of [Co/Pt]₃/Co.

FIGS. 5A to 5C correspond to a case where the four ferromagneticconstituent layers has the same film thickness.

FIG. 5A shows an example in which the film thickness of the threenonmagnetic constituent layers gradually becomes smaller as it goes fromthe uppermost layer to the lowest layer. Among film-thickness magnituderelationships described on a right side in FIG. 5A, the uppermostmagnitude relationship corresponds to FIG. 5A, and the other threemagnitude relationships correspond to modification examples of FIG. 5A.

A configuration of FIG. 5B is an example in which the film thicknessgradually becomes larger as it goes from the uppermost layer to thelowest layer. Among film-thickness magnitude relationships described ona right side in FIG. 5B, the uppermost magnitude relationshipcorresponds to FIG. 5B, and the other three magnitude relationshipscorrespond to modification examples of FIG. 5B.

A configuration of FIG. 5C is an example in which arrangement of thefilm thickness does not follow a large film thickness order or a smallfilm thickness order. Among film-thickness relationships described on aright side in FIG. 5C, the uppermost relationship corresponds to FIG.5C, and the other two relationships correspond to modification examplesof FIG. 5C.

FIGS. 5D to 5F correspond to a case where the three nonmagneticconstituent layers have the same film thickness.

FIG. 5D shows an example in which the film thickness of the fourferromagnetic constituent layers gradually becomes smaller as it goesfrom the uppermost layer to the lowest layer. Among film-thicknessmagnitude relationships described on a right side in FIG. 5D, theuppermost magnitude relationship corresponds to FIG. 5D, and the otherthree magnitude relationships correspond to modification examples ofFIG. 5D.

A configuration of FIG. 5E is an example in which the film thicknessgradually becomes larger as it goes from the uppermost layer to thelowest layer. In film-thickness magnitude relationship described on aright side in FIG. 5E, the uppermost magnitude relationship correspondsto FIG. 5E, and the other three magnitude relationships correspond tomodification examples of FIG. 5E.

A configuration of FIG. 5F is an example in which arrangement of thefilm thickness does not follow a large film thickness order or a smallfilm thickness order. Among film-thickness relationships described on aright side in FIG. 5F, the uppermost relationship corresponds to FIG.5F, and the other two relationships correspond to modification examplesof FIG. 5F.

In the spin current magnetization rotational element of the embodiment,with respect to an average film thickness (simple average filmthickness) of the plurality of ferromagnetic constituent layers, thefilm thickness of each of the ferromagnetic constituent layers may bedifferent from the average film thickness by ±10% or more, or withrespect to an average film thickness of the plurality of nonmagneticconstituent layers, a film thickness of each of the nonmagneticconstituent layers may be different from the average film thickness ofthe nonmagnetic constituent layers by ±10% or more.

In layers having film thicknesses different from each other, when eachof the film thicknesses is different from the average film thickness by10% or more, an effect is further enhanced.

In the spin current magnetization rotational element of the embodiment,sheet resistance of the first ferromagnetic metal layer may be smallerthan sheet resistance of the spin-orbit torque wiring.

When the sheet resistance of the first ferromagnetic metal layer issmaller than the sheet resistance of the spin-orbit torque wiring, acurrent is likely to invade into the first ferromagnetic metal layer.

It is preferable that a material of the ferromagnetic constituent layersis selected from ferromagnetic metals including any one of Fe, Co, andNi, and a material of the nonmagnetic constituent layers is selectedfrom nonmagnetic metals including any one of Ti, Cr, Cu, Mo, Ru, Rh, Pd,Ag, Hf, Ta, W, Ir, Pt, Au, and Bi.

It is preferable that a ratio of a length of the first ferromagneticmetal layer along the second direction to the thickness of the firstferromagnetic metal layer is 1 or greater, more preferably 5 or greater,and still more preferably 10 or greater.

Among currents, which invade into the first ferromagnetic metal layerfrom the spin-orbit torque wiring, in a current that goes around faraway from the spin-orbit torque wiring, resistance further increases.However, as the ratio of the length of the first ferromagnetic metallayer to the thickness of the first ferromagnetic metal layer increases,it is possible to suppress an influence on an increase in resistance dueto detouring.

As to be described later, the spin current magnetization rotationalelement of the embodiment is applicable to a magnetoresistance effectelement. The use is not limited to the magnetoresistance effect element,and application to another use is also possible. With regard to theother use, for example, the spin current magnetization rotationalelement may be used in a spatial optical modulator in which the spincurrent magnetization rotational element is arranged in respectivepixels to spatially modulate incident light by using a magneto-opticaleffect. In addition, a magnetic field, which is applied to an axis ofeasy magnetization of a magnet to avoid a hysteresis effect due tocoercivity of the magnet in a magnetic sensor, may be substituted withSOT.

Magnetoresistance Effect Element

A magnetoresistance effect element according an embodiment of thedisclosure includes the spin current magnetization rotational element ofthe embodiment, a second ferromagnetic metal layer in which amagnetization direction is fixed, and a nonmagnetic layer that isinterposed between the first ferromagnetic metal layer and the secondferromagnetic metal layer.

Here, fixing of the magnetization direction represents that amagnetization direction does not vary (magnetization is fixed) beforeand after recoding by using a recording current.

It is preferable that among a plurality of ferromagnetic constituentlayers of the first ferromagnetic metal layer, the film thickness of aferromagnetic constituent layer that is in contact with the nonmagneticlayer is smallest.

The reason for this is that the interface-orthogonal magneticanisotropy, which acts on between the nonmagnetic layers and theferromagnetic constituent layers, can be maximized.

FIG. 6 is an application example of the spin current magnetizationrotational element of the embodiment, and is a perspective viewschematically showing a magnetoresistance effect element that is alsothe magnetoresistance effect element according to an embodiment of thedisclosure. Furthermore, in FIG. 6, characteristic portions of the spincurrent magnetization rotational element of the embodiment are notshown.

A magnetoresistance effect element 100 shown in FIG. 6 includes the spincurrent magnetization rotational element (a first ferromagnetic metallayer 101 and a spin-orbit torque wiring 120) of the embodiment, asecond ferromagnetic metal layer 103 in which a magnetization directionis fixed, and a nonmagnetic layer 102 that is interposed between thefirst ferromagnetic metal layer 101 and the second ferromagnetic metallayer 103. The first ferromagnetic metal layer 101 has the sameconfiguration as in the first ferromagnetic metal layer 1, and thespin-orbit torque wiring 120 has the same configuration as in thespin-orbit torque wiring 2. In addition, it can be said that themagnetoresistance effect element 100 shown in FIG. 6 includes amagnetoresistance effect element part 105 and the spin-orbit torquewiring 120.

The magnetoresistance effect element according to an embodiment of theembodiment may have a configuration in which magnetization reversal ofthe magnetoresistance effect element is performed with SOT alone due tothe pure spin current (hereinafter, may be referred to as “SOT-alone”configuration), or a configuration in which in the magnetoresistanceeffect element using STT in the related art, SOT due to the pure spincurrent is used in combination.

In the following description including FIG. 6, as an example of aconfiguration in which the spin-orbit torque wiring extends in adirection intersecting a lamination direction of the magnetoresistanceeffect element part, description will be given of a case of aconfiguration extending in an orthogonal direction.

In FIG. 6, a wiring 130 through which a current flows in the laminationdirection of the magnetoresistance effect element 100, and a substrate110 that forms the wiring 130 are also shown. In addition, a cap layer104 is provided between the first ferromagnetic metal layer 101 and thespin-orbit torque wiring 120.

Magnetoresistance Effect Element Part

The magnetoresistance effect element part 105 includes the secondferromagnetic metal layer 103 in which a magnetization direction isfixed, the first ferromagnetic metal layer 101 in which a magnetizationdirection varies, and the nonmagnetic layer 102 that is interposedbetween the second ferromagnetic metal layer 103 and the firstferromagnetic metal layer 101.

Since magnetization of the second ferromagnetic metal layer 103 is fixedin one direction, and the magnetization direction of the firstferromagnetic metal layer 101 relatively varies, a function as themagnetoresistance effect element part 105 is also possible. In anapplication to coercivity difference type (pseudo spin valve type) MRAM,coercivity of the second ferromagnetic metal layer is greater thancoercivity of the first ferromagnetic metal layer, and in an applicationto an exchange bias type (spin valve type) MRAM, in the secondferromagnetic metal layer, the magnetization direction is fixed due toexchange coupling with an antiferromagnetic layer.

In addition, in a case where the nonmagnetic layer 102 is formed from aninsulator, the magnetoresistance effect element part 105 is a tunnelingmagnetoresistive element (TMR) element, and in a case where thenonmagnetic layer 102 is formed from a metal, the magnetoresistanceeffect element part 105 is a giant magnetoresistive (GMR) element.

With regard to the magnetoresistance effect element part that isprovided in the embodiment, a configuration of a magnetoresistanceeffect element part of the related art can be used. For example, eachlayer may include a plurality of layers, or another layer such as anantiferromagnetic layer configured to fix the magnetization direction ofthe second ferromagnetic metal layer may be provided.

The second ferromagnetic metal layer 103 and the first ferromagneticmetal layer 101 may be an in-plane magnetic film in which themagnetization direction is an in-plane direction parallel to a layer, oran orthogonal magnetic film in which the magnetization direction is adirection orthogonal to a layer.

As a material of the second ferromagnetic metal layer 103, a knownmaterial can be used. For example, a metal that is selected from thegroup consisting of Cr, Mn, Co, Fe, and Ni, and alloys which include oneor more kinds of the metals and exhibit ferromagnetism can be used. Inaddition, alloys which include the metals, and at least one or morekinds of elements among B, C, and N, can be used. Specific examplesthereof include Co—Fe, and Co—Fe—B.

In addition, it is preferable to use a Heusler alloy such as Co₂FeSi toobtain a relatively higher output. The Heusler alloy includes anintermetallic compound having a chemical composition of X₂YZ. Here, Xrepresents a transition metal element or a noble metal element of agroup of Co, Fe, Ni, or Cu in a periodic table, Y represents atransition metal of a group of Mn, V, Cr, or Ti and can also employelement species of X, and Z is a typical element of a group III to agroup V. Examples of the Heusler alloy include Co₂FeSi, Co₂MnSi,Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b), and the like.

In addition, to further increase coercivity with respect to the firstferromagnetic metal layer 101 of the second ferromagnetic metal layer103, as a layer (pinning layer) that is in contact with the secondferromagnetic metal layer 103 on a surface opposite to a surface that isin contact with the nonmagnetic layer 102, a layer of anantiferromagnetic material such as IrMn and PtMn may be used. Inaddition, it is possible to employ a synthetic ferromagnetic couplingstructure so that a leakage magnetic field of the second ferromagneticmetal layer 103 does not have an effect on the first ferromagnetic metallayer 101.

In addition, in a case where the magnetization direction of the secondferromagnetic metal layer 103 is set to orthogonal to a laminationsurface, it is preferable to use a laminated film of Co and Pt.Specifically, the second ferromagnetic metal layer 103 may be set to [Co(0.24 nm)/Pt (0.16 nm)]6/Ru (0.9 nm)/[Pt (0.16 nm)/Co (0.16 nm)]4/Ta(0.2 nm)/FeB (1.0 nm).

A known material can be used for the nonmagnetic layer 102. For example,in a case where the nonmagnetic layer 102 is formed from an insulator(that is, in a case of a tunnel barrier layer), as a material thereof,Al₂O₃, SiO₂, Mg, and MgAl₂O₄ and the like can be used. In addition, inaddition to these materials, materials in which a part of Al, Si, and Mgis substituted with Zn, Be, and the like, and the like can be used.Among these, MgO or MgAl₂O₄ is a material capable of realizing acoherent tunnel, and thus it is possible to efficiently inject a spin.In addition, in a case where the nonmagnetic layer 102 is formed from ametal, as a material thereof, Cu, Au, Ag, and the like can be used.

In addition, it is preferable that the cap layer 104 is formed on asurface opposite to the nonmagnetic layer 102 of the first ferromagneticmetal layer 101 as shown in FIG. 6. The cap layer 104 can suppressdiffusion of elements from the first ferromagnetic metal layer 101. Inaddition, the cap layer 104 also contributes to a crystal orientation ofeach layer of the magnetoresistance effect element part 105. As aresult, when the cap layer 104 is provided, magnetism of the secondferromagnetic metal layer 103 and the first ferromagnetic metal layer101 of the magnetoresistance effect element part 105 is stabilized, andthus it is possible to realize a reduction in resistance of themagnetoresistance effect element part 105.

In the cap layer 104, a high-conductivity material is preferably used.For example, Ru, Ta, Cu, Ag, Au, and the like can be used. It ispreferable that a crystal structure of the cap layer 104 isappropriately set to a face centered cubic (fcc) structure, a hexagonalclosest packing (hcp) structure, or a body centered cubic (bcc)structure in accordance with a crystal structure of the ferromagneticmetal layer that is adjacent to the cap layer 104.

In addition, it is preferable to use any one selected from the groupconsisting of Ag, Cu, Mg, and Al in the cap layer 104. Although detailswill be described later, in a case where the spin-orbit torque wiring120 and the magnetoresistance effect element part 105 are connectedthrough the cap layer 104, it is preferable that the cap layer 104 doesnot scatter a spin that propagates from the spin-orbit torque wiring120. It is known that silver, copper, magnesium, aluminum, and the likehas a spin diffusion length as long as 100 nm or greater, and thus thespin is less likely to be scattered.

It is preferable that the thickness of the cap layer 104 is equal to orless than a spin diffusion length of a material that constitutes the caplayer 104. When the thickness of the cap layer 104 is equal to or lessthan the spin diffusion length, it is possible to sufficiently transferthe spin that propagates from the spin-orbit torque wiring 120 to themagnetoresistance effect element part 105.

Substrate

It is preferable that the substrate 110 is excellent in flatness. Toobtain a surface with excellent flatness, it is possible to use amaterial, for example, Si, AlTiC, and the like.

An underlayer (not shown) may be formed on a surface of the substrate110 on the magnetoresistance effect element part 105 side. When theunderlayer is provided, it is possible to control crystallinity such asa crystal orientation and a crystal grain size of respective layersincluding the second ferromagnetic metal layer 103 that is laminated onthe substrate 110.

It is preferable that the underlayer has an insulating property in orderfor a current flowing to a wiring 130 and the like not to be scattered.As the underlayer, various layers can be used. For example, as oneexample, a nitride layer, which has a (001)-oriented NaCl structure andincludes at least one element selected from the group consisting of Ti,Zr, Nb, V, Hf, Ta, Mo, W, B, Al, and Ce, can be used in the underlayer.

As another example, it is possible to use a (002)-orientedperovskite-based conductive oxide layer expressed by a compositionformula of XYO₃ can be used in the underlayer. Here, a site X includesat least one element selected from the group consisting of Sr, Ce, Dy,La, K, Ca, Na, Pb, and Ba, and a site Y includes at least one elementthat is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni,Ga, Nb, Mo, Ru, Ir, Ta, Ce, and Pb.

As still another example, it is possible to use an oxide layer that hasa (001)-oriented NaCl structure and includes at least one elementselected from the group consisting of Mg, Al, and Ce in the underlayer.

As still another example, it is possible to use a layer that has a(001)-oriented tetragonal structure or cubic structure, and includes atleast one element selected from the group consisting of Al, Cr, Fe, Co,Rh, Pd, Ag, Ir, Pt, Au, Mo, and W as the underlayer.

In addition, the underlayer is not limited to a monolayer, and aplurality of layers in the examples may be laminated. Throughexamination of a configuration of the underlayer, it is possible toenhance crystallinity of each layer of the magnetoresistance effectelement part 105, and thus it is possible to improve magneticcharacteristics.

Wiring

The wiring 130 is electrically connected to the second ferromagneticmetal layer 103 of the magnetoresistance effect element part 105, and inFIG. 6, the wiring 130, the spin-orbit torque wiring 120, and a powersupply (not shown) constitute a closed circuit, and thus a current flowsin a lamination direction of the magnetoresistance effect element part105.

A material of the wiring 130 is not particularly limited as long as thematerial has high conductivity. For example, aluminum, silver, copper,gold, and the like can be used.

In the embodiment, description has been given of an example of aso-called bottom pin structure in which in the magnetoresistance effectelement 100, the first ferromagnetic metal layer 101 that is laminatedlater and is disposed on a side far away from the substrate 110 becomesa magnetization-free layer, and the second ferromagnetic metal layer 103that is laminated first and is disposed on a side close to the substrate110 becomes a magnetization fixed layer (pin layer), but the structureof the magnetoresistance effect element 100 is not particularly limited,and a so-called top pin structure is also possible.

Power Supply

The magnetoresistance effect element 100 further includes a first powersupply 140 that allows a current to flow in the lamination direction ofthe magnetoresistance effect element part 105, and a second power supply150 that allows a current to flow to the spin-orbit torque wiring 120.

The first power supply 140 is connected to the wiring 130 and thespin-orbit torque wiring 120. The first power supply 140 can control acurrent that flows in the lamination direction of the magnetoresistanceeffect element 100.

The second power supply 150 is connected to both ends of the spin-orbittorque wiring 120. The second power supply 150 can control a currentthat is a current that flows in a direction orthogonal to the laminationdirection of the magnetoresistance effect element part 105, that is, acurrent that flows to the spin-orbit torque wiring 120.

As described above, the current that flows in the lamination directionof the magnetoresistance effect element part 105 causes STT. Incontrast, the current that flows to the spin-orbit torque wiring 120causes SOT. Both of the STT and the SOT contribute to magnetizationreversal of the first ferromagnetic metal layer 101.

As described above, the amount of currents, which respectively flow inthe lamination direction of the magnetoresistance effect element part105 and in a direction orthogonal to the lamination direction, iscontrolled by the two power supplies, and thus it is possible to freelycontrol contribution rates of the SOT and the STT with respect to themagnetization reversal.

For example, in a case where it is difficult to flow a large current toa device, a control may be performed so that the STT with high energyefficiency with respect to the magnetization reversal becomes a maintype. That is, the amount of current that flows from the first powersupply 140 may be increased, and the amount of current that flows fromthe second power supply 150 may be decreased.

In addition, for example, in a case where it is necessary to prepare athin device, and thus it is necessary to make the thickness of thenonmagnetic layer 102 be small, it is required to reduce a current thatflows to the nonmagnetic layer 102. In this case, the amount of currentthat flows from the first power supply 140 may be reduced, and theamount of current that flows from the second power supply 150 may beincreased to enhance the contribution rate of the SOT.

A known power supply can be used as the first power supply 140 and thesecond power supply 150.

As described above, according to the magnetoresistance effect element ofthe embodiment in a case of the configuration using the STT type and theSOT type in combination, the contribution rate of the STT and the SOTcan be freely controlled by the amount of currents which are suppliedfrom the first power supply and the second power supply. According tothis, it is possible to freely control the contribution rate of the STTand the SOT in correspondence with a performance that is required for adevice, and thus the magnetoresistance effect element can function as amagnetoresistance effect element with relatively high general-purposeproperties.

Manufacturing Method

A method of manufacturing the spin current magnetization rotationalelement and the magnetoresistance effect element including the spincurrent magnetization rotation element according to the embodiment isnot particularly limited, and a known film formation method can be used.With regard to the film formation method, for example, as a physicalvapor deposition (PVD) method, resistive heating deposition, electronbeam deposition, a molecular beam epitaxy (MBE) method, an ion platingmethod, an ion beam deposition method, a sputtering method, and the likecan be used. Alternatively, as a chemical vapor deposition (CVD) method,a thermal CVD method, an optical CVD method, a plasma CVD method, ametalorganic chemical vapor deposition (MOCVD), an atomic layerdeposition (ALD) method, and the like can be used. In addition, a singleatom layer doping method (delta doping method) can be used to form avery thin interface spin generation layer having a thickness that isapproximately two or less times an atomic radius.

The spin-orbit torque wiring and the first ferromagnetic metal layer canbe formed, for example, by using a magnetron sputtering apparatus. Afterfilm formation, a resist or a protective film is provided on a portionat which the spin current magnetization rotational element is desired tobe prepared, and an unnecessary portion is removed by using an ionmilling method or a reactive ion etching (RIE) method.

In the first ferromagnetic metal layer, to enlarge a cross-sectionalarea of a cross-section orthogonal to a plane-orthogonal direction as itbecomes closer to the spin-orbit torque wiring, an apparatus including amechanism capable of changing a relative angle (angle θ from the z-axis)between an ion irradiation direction in the ion milling or RIE, and thespin current magnetization rotational element 10 is used. A technologycapable of forming an element with good horny ratio or an element havinga truncated shape by changing the relative angle of the ion irradiationwith respect to the spin current magnetization rotational element 10 isknown.

In addition, in a case where the spin-orbit torque wiring includes thepure spin current generating portion and the low-resistance portion, arelative angle is fixed to 30° to 80° with respect to a spin currentmagnetization reversal laminated film that is provided with a resist ora protective film, and the spin generating portion is milled. Accordingto this, it is possible to form a spin generating portion having alinear inclination. In addition, it is possible to form a spingenerating portion having a curved inclination by performing millingwhile changing the relative angle during the milling. Then, thelow-resistance portion is formed, a resist or a protective film isprovided, and then milling is performed. According to this, it ispossible to form the low-resistance portion in a shape of the spin-orbittorque wiring.

For example, when preparing the magnetoresistance effect element byusing a sputtering method, in a case where the magnetoresistance effectelement is the TMR element, for example, a tunnel barrier layer isformed as follows. First, a metal thin film including magnesium,aluminum, and divalent cations of a plurality of nonmagnetic elements issputtered onto the first ferromagnetic metal layer in a thickness ofapproximately 0.4 to 2.0 nm, and plasma oxidation or natural oxidationdue to instruction of oxygen is performed. Then, a heat treatment isperformed.

It is preferable that the resultant laminated film that is obtained issubjected to an annealing treatment. A layer that is formed throughreactive sputtering is amorphous, and thus it is necessary tocrystallize the layer. For example, in a case of using Co—Fe—B as theferromagnetic metal layer, a part of B is leaked due to the annealingtreatment, and thus the layer is crystallized.

In the magnetoresistance effect element that is prepared through theannealing treatment, a magnetoresistance ratio is further improved incomparison to a magnetoresistance effect element that is preparedwithout being subjected to the annealing treatment. The reason for thisis considered to be because uniformity in a crystal size and orientationof the tunnel barrier layer of the nonmagnetic layer are improved due tothe annealing treatment.

With regard to the annealing treatment, it is preferable that heating isperformed at a temperature of 300° C. to 500° C. for 5 minutes to 100minutes in an inert atmosphere such as Ar, and heating is performed at atemperature of 100° C. to 500° C. for 1 hour to 10 hours in a state inwhich a magnetic field of 2 kOe to 10 kOe is applied.

As a method of shaping the magnetoresistance effect element into apredetermined shape, a processing method such as photolithography can beused. First, the magnetoresistance effect element is laminated, and asurface, which is opposite to the spin-orbit torque wiring, of themagnetoresistance effect element is coated with a resist. Then, theresist in a predetermined portion is cured to remove the resist in anunnecessary portion. A portion in which the resist is cured becomes aprotective film of the magnetoresistance effect element. The portion inwhich the resist is cured matches the shape of the magnetoresistanceeffect element that is finally obtained.

In addition, the surface on which the protective film is formed issubjected to a treatment such as ion milling and reactive ion etching(RIE). A portion in which the protective film is not formed is removed,and thus a magnetoresistance effect element having a predetermined shapeis obtained.

Magnetic Memory

A magnetic memory (MRAM) of the embodiment includes a plurality of themagnetoresistance effect elements of the embodiment.

The thickness of each layer can be measured, for example, by a TEM or aperiod of peaks in element analysis.

EXPLANATION OF REFERENCES

-   -   1 First ferromagnetic metal layer    -   2 Spin-orbit torque wiring    -   10 spin current magnetization rotational element (spin current        magnetization reversal element)    -   100 Magnetoresistance effect element    -   101 First ferromagnetic metal layer    -   102 Nonmagnetic layer    -   103 Second ferromagnetic metal layer    -   104 Cap layer    -   105 Magnetoresistance effect element unit    -   110 Substrate    -   120 Spin-orbit torque wiring    -   130 Wiring    -   140 First power supply    -   150 Second power supply

What is claimed is:
 1. A spin current magnetization rotational element,comprising: a first ferromagnetic metal layer in which a magnetizationdirection is variable; and a spin-orbit torque wiring that extends in asecond direction intersecting a first direction that is aplane-orthogonal direction of the first ferromagnetic metal layer, andis joined to the first ferromagnetic metal layer, wherein the firstferromagnetic metal layer has a lamination structure including aplurality of ferromagnetic constituent layers and a plurality ofnonmagnetic constituent layers which are respectively interposed betweenthe ferromagnetic constituent layers adjacent to each other, and atleast one ferromagnetic constituent layer among the plurality offerromagnetic constituent layers has a film thickness different from afilm thickness of the other ferromagnetic constituent layers, and/or atleast one nonmagnetic constituent layer among the plurality ofnonmagnetic constituent layers has a film thickness different from afilm thickness of the other nonmagnetic constituent layers.
 2. The spincurrent magnetization rotational element according to claim 1, whereinfilm thicknesses of two ferromagnetic constituent layers, between whichone nonmagnetic constituent layer among the plurality of nonmagneticconstituent layers is interposed, among the plurality of ferromagneticconstituent layers are different from each other, or film thicknesses oftwo nonmagnetic constituent layers, between which one ferromagneticconstituent layer among the plurality of ferromagnetic constituentlayers is interposed, among the plurality of nonmagnetic constituentlayers are different from each other.
 3. The spin current magnetizationrotational element according to claim 1, wherein among the plurality ofnonmagnetic constituent layers, a nonmagnetic laminated layer that isthe closest to the spin-orbit torque wiring is thinner than the othernonmagnetic laminated layers.
 4. The spin current magnetizationrotational element according to claim 3, wherein among the plurality offerromagnetic constituent layers, a ferromagnetic constituent layer thatis closest to the spin-orbit torque wiring is thinner than the otherferromagnetic constituent layers.
 5. The spin current magnetizationrotational element according to claim 3, wherein, with respect to anaverage film thickness of the plurality of ferromagnetic constituentlayers, a film thickness of each of the ferromagnetic constituent layersis different from the average film thickness by ±10% or more, or withrespect to an average film thickness of the plurality of nonmagneticconstituent layers, a film thickness of each of nonmagnetic laminatedlayers is different from the average film thickness of the nonmagneticlaminated layers by ±10% or more.
 6. The spin current magnetizationrotational element according to claim 1, wherein among the plurality ofnonmagnetic constituent layers, a material of at least one nonmagneticconstituent layer is different from a material of the other nonmagneticconstituent layers.
 7. The spin current magnetization rotational elementaccording to claim 6, wherein among the plurality of ferromagneticconstituent layers, a ferromagnetic constituent layer that is closest tothe spin-orbit torque wiring is thinner than the other ferromagneticconstituent layers.
 8. The spin current magnetization rotational elementaccording to claim 1, wherein the nonmagnetic constituent layers areformed from a material that applies interface-orthogonal magneticanisotropy to the ferromagnetic constituent layers.
 9. The spin currentmagnetization rotational element according to claim 1, wherein among theplurality of ferromagnetic constituent layers, a ferromagneticconstituent layer that is closest to the spin-orbit torque wiring isthinner than the other ferromagnetic constituent layers.
 10. The spincurrent magnetization rotational element according to claim 9, whereinany one ferromagnetic constituent layer among the plurality offerromagnetic constituent layers includes a dead layer.
 11. The spincurrent magnetization rotational element according to claim 9, wherein,with respect to an average film thickness of the plurality offerromagnetic constituent layers, a film thickness of each of theferromagnetic constituent layers is different from the average filmthickness by ±10% or more, or with respect to an average film thicknessof the plurality of nonmagnetic constituent layers, a film thickness ofeach of nonmagnetic laminated layers is different from the average filmthickness of the nonmagnetic laminated layers by ±10% or more.
 12. Thespin current magnetization rotational element according to claim 1,wherein any one ferromagnetic constituent layer among the plurality offerromagnetic constituent layers includes a dead layer.
 13. The spincurrent magnetization rotational element according to claim 1, wherein,with respect to an average film thickness of the plurality offerromagnetic constituent layers, a film thickness of each of theferromagnetic constituent layers is different from the average filmthickness by ±10% or more, or with respect to an average film thicknessof the plurality of nonmagnetic constituent layers, a film thickness ofeach of nonmagnetic laminated layers is different from the average filmthickness of the nonmagnetic laminated layers by ±10% or more.
 14. Thespin current magnetization rotational element according to claim 1,wherein as the first ferromagnetic metal layer is closer to thespin-orbit torque wiring, a cross-sectional area of a cross-section thatis orthogonal to the first direction is enlarged.
 15. The spin currentmagnetization rotational element according to claim 1, wherein sheetresistance of the first ferromagnetic metal layer is smaller than sheetresistance of the spin-orbit torque wiring.
 16. The spin currentmagnetization rotational element according to claim 1, wherein amaterial of the ferromagnetic constituent layers is selected fromferromagnetic metals including any one of Fe, Co, and Ni, and a materialof the nonmagnetic constituent layers is selected from nonmagneticmetals including any one of Ti, Cr, Cu, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W,Ir, Pt, Au, and Bi.
 17. The spin current magnetization rotationalelement according to claim 1, wherein a ratio of a length of the firstferromagnetic metal layer along the second direction to the thickness ofthe first ferromagnetic metal layer is 1 or greater.
 18. Amagnetoresistance effect element, comprising: the spin currentmagnetization rotational element according to claim 1; a secondferromagnetic metal layer in which a magnetization direction is fixed;and a nonmagnetic layer that is interposed between the firstferromagnetic metal layer and the second ferromagnetic metal layer. 19.The magnetoresistance effect element according to claim 18, whereinamong the plurality of ferromagnetic constituent layers, a filmthickness of a ferromagnetic constituent layer that is in contact withthe nonmagnetic layer is the smallest.
 20. A magnetic memory,comprising: a plurality of the magnetoresistance effect elementsaccording to claim 18.